Stresses appearing during rock breaking in a rock breaking system may be measured and employed in controlling the rock breaking. FI69680 and U.S. Pat. No. 4,671,366 disclose an example of measuring stress waves appearing during rock breaking and employing the measured stress waves in controlling the operation of a rock breaking device. DE19932838 and U.S. Pat. No. 6,356,077 disclose a signal processing method and device for determining a parameter of a stress wave by measuring magnetoelastic changes caused by stress waves in a component of the rock breaking system subjected to percussive loads.
For example, in U.S. Pat. No. 6,356,077 the stress waves appearing during rock breaking are measured by measuring changes in a magnetic property of the rock breaking system component. For the measurement of the stress waves the rock breaking system component is subjected to an external magnetic field by a magnetizing coil simultaneously during the measurement of the stress waves. Subjecting the rock breaking system component to the external magnetic field simultaneously with the measurement of the stress waves will, however, cause disturbances in the measurement results regardless of the instrumentation configuration.
In EP-publication 2811110 at least part of the component of the rock breaking system component is arranged into a state of persistent or remanent magnetization. With this solution the above mentioned problems relating to the simultaneous magnetizing of the rock breaking system component and measurement of the stress waves may be avoided. The arrangement of the rock breaking system component into the state of persistent or remanent magnetization does not necessarily as such provide accurate stress wave measurement results, or results accurate enough to be used for monitoring or controlling the operation of the rock breaking device.